What is Hyundai R335LC-9T Fault Code 111-3?

Fault Code 111-3 on the Hyundai R335LC-9T excavator indicates an Engine Coolant Temperature (ECT) Sensor Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the coolant temperature sensor circuit, typically exceeding 4.8-4.9 volts when normal operating range should be 0.5-4.5 volts.

This code directly affects the ECM's ability to manage critical engine functions including fuel injection timing, engine warm-up cycles, and cooling fan operation. On the R335LC-9T's Cummins QSB6.7 engine, accurate coolant temperature readings are essential for optimal performance and preventing overheating damage. When this fault activates, the ECM enters a default mode using predetermined temperature values, which can lead to reduced fuel efficiency and potential engine protection derate.

Common Symptoms

• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument cluster
• Engine may experience rough idling or hard starting conditions, especially when cold
• Cooling fan runs continuously at high speed regardless of actual engine temperature
• Reduced engine power or automatic derate to 1,500 RPM in severe cases
• Inaccurate coolant temperature gauge readings showing maximum temperature despite cool engine

Potential Causes

The high voltage condition in Code 111-3 most commonly results from an open circuit in the sensor wiring or sensor itself. On used R335LC-9T excavators, the primary causes include:

• Failed ECT sensor with internal open circuit (common after 5,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at the engine valley harness routing point where rubbing against valve cover edges occurs
• Loose or corroded connector pins at the ECT sensor or ECM connection points
• Broken signal wire within the main engine harness due to vibration fatigue
• Rare: ECM internal circuit failure on the temperature sensor input channel

How to Troubleshoot and Fix Code 111-3

Step 1: Visual Inspection and Connector Check Begin by locating the ECT sensor on the cylinder head (driver's side, near thermostat housing). Disconnect the two-pin connector and inspect for corrosion, bent pins, or moisture intrusion. On used excavators, this connector frequently develops white/green corrosion due to coolant weeping. Clean contacts with electrical contact cleaner and examine the harness for chafing marks along the valve cover edge.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure resistance across the ECT sensor terminals. At 68°F (20°C), resistance should read approximately 2,400-2,700 ohms. An infinite (OL) reading indicates an open sensor requiring replacement. Compare readings against the temperature-resistance chart in the Hyundai service manual for verification.

Step 3: Circuit Voltage Testing With the sensor disconnected and ignition ON (engine off), backprobe the harness connector. Measure voltage on the 5-volt reference wire (should read 4.8-5.2V) and verify the signal ground wire shows less than 0.1 volts to chassis ground. If reference voltage is missing, trace the harness back to the ECM connector C101 checking for breaks or shorts.

Step 4: Harness Continuity and Insulation Check Perform a continuity test from the sensor connector to ECM pins (refer to wiring diagram for pin identification). Check for less than 5 ohms resistance on each wire. Additionally, test insulation resistance to ground on both wires—readings should exceed 10 megohms. Values below this indicate insulation breakdown from harness chafing, common where the harness passes near exhaust components.

Step 5: Replace Components and Clear Code After identifying the fault, replace the ECT sensor (Hyundai part number 39210-45000 or equivalent) using proper thread sealant rated for coolant contact. If harness damage exists, repair using heat-shrink solder connectors and relocate away from abrasion points using proper stand-offs. Clear the code using Hyundai diagnostic software or compatible J1939 scan tool and verify the fault does not return after a complete warm-up cycle.

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Disclaimer: This guide provides general troubleshooting information for Hyundai R335LC-9T excavators. Always consult the manufacturer's service manual and qualified diesel technicians for specific repair procedures. Electrical diagnostics should only be performed by trained personnel with appropriate safety equipment.